WalletConnect

Content disclaimer

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WalletConnect is an open protocol - not a wallet - built to create a communication link between dApps and wallets. A wallet and an application supporting this protocol will enable a secure link through a shared key between any two peers. A connection is initiated by the dApp displaying a QR code with a standard WalletConnect URI and the connection is established when the wallet application approves the connection request. Further requests regarding funds transfer are confirmed on the wallet application itself.

Set up web3

To set up your dApp to connect with a user’s Polygon Wallet, you can use WalletConnect’s provider to directly connect to Polygon. Install the following in your dApp:

npm install --save @maticnetwork/walletconnect-provider

Install matic.js for Polygon integration:

npm install @maticnetwork/maticjs

And add the following code in your dApp;

import WalletConnectProvider from "@maticnetwork/walletconnect-provider"

import Web3 from "web3"
import Matic from "maticjs"

Next, set up Polygon and Ropsten provider via WalletConnect’s object:

const maticProvider = new WalletConnectProvider(
  {
    host: `https://rpc-mumbai.matic.today`,
    callbacks: {
      onConnect: console.log('connected'),
      onDisconnect: console.log('disconnected!')
    }
  }
)

const ropstenProvider = new WalletConnectProvider({
  host: `https://ropsten.infura.io/v3/70645f042c3a409599c60f96f6dd9fbc`,
  callbacks: {
    onConnect: console.log('connected'),
    onDisconnect: console.log('disconnected')
  }
})

We created the above two provider objects to instantiate our Web3 object with:

const maticWeb3 = new Web3(maticProvider)
const ropstenWeb3 = new Web3(ropstenProvider)

Instantiating contracts

Once we have our web3 object, the instantiating of contracts involves the same steps as for Metamask. Make sure you have your contract ABI and address already in place.

const myContractInstance = new this.maticWeb3.eth.Contract(myContractAbi, myContractAddress)

Calling functions

Info

The private key will remain in the user’s wallet and the app does not access it in any way.

We have two types of functions in Ethereum, depending upon the interaction with the blockchain. We call() when we read data and send() when we write data.

Calling call() functions

Reading data doesn’t require a signature, therefore the code should be like this:

this.myContractInstance.methods
  .myMethod(myParams)
  .call()
  .then (
  // do stuff with returned values
  )

Calling send() functions

Since writing to the blockchain requires a signature, we prompt the user on their wallet (that supports WalletConnect) to sign the transaction.

This involves three steps:

1. Constructing a transaction
2. Getting a signature on the transaction
3. Sending signed transaction

const tx = {
  from: this.account,
  to: myContractAddress,
  gas: 800000,
  data: this.myContractInstance.methods.myMethod(myParams).encodeABI(),
}

The above code creates a transaction object which is then sent to user’s wallet for signature:

maticWeb3.eth.signTransaction(tx)
  .then((result) =>{
    maticWeb3.eth.sendSignedTransaction(result)
    .then((receipt) =>
    console.log (receipt)
  )
})

signTransaction() function prompts the user for their signature and sendSignedTransaction() sends the signed transaction (returns a transaction receipt on success).